This invention pertains generally to spring loaded relief valves used in hydraulic systems. More particularly the invention relates to such valves which are used to equalize the pressure between two single acting hydraulic jacks such as used in backing support for a snowplow blade or the like.
Valves of this general type are frequently referred to as "crossover" valves. For instance, in a plow application where two jacks are used as backing support for opposite ends of the plow and one end of the plow encounters an obstruction to cause contracting pressure on the jack at that end, the valve will be forced open to allow fluid to flow from the contracting jack into the cylinder of the other jack. This is a normal operation as the plow is generally pivoted at a central point to a motive power frame whereby upon contraction of one jack the other jack will be in an extending condition and thus receptive to additional fluid.
However, in certain conditions when one or both ends of the plow blade encounter heavy resistance, a retracting cylinder may exhaust more fluid than the other cylinder can accept. This may create excessive pressure in one or both cylinders and the fluid lines leading thereto with resultant damage to the hydraulic system.